There is known from Swiss Patent No. 20552 in the name of J. L. Kurtz, filed on 1 Nov. 1899, a balance bar associated with means for adjusting the relative position of the two bearings in which the two ends of the balance staff or arbour respectively pivot. The balance bar described is of the simple type, i.e. with a single base secured to a bottom plate and a plate connected to one end of this single base and having at its other free end an aperture for arranging a bearing. The balance bar is secured to the bottom plate by a single screw passing right through the single base.
In this patent, the shake of the balance staff is adjusting by adjusting the height of the balance bar plate. Three regulating screws are provided for this purpose on the periphery of the tightening screw. The three regulating screws pass through the base of the bar and abut on the side of the bottom plate against three other complementary screws defining thus three points of abutment for the three adjusting screws. By screwing or unscrewing the three adjusting screws in a homogenous manner, it is thus possible to vary the height of the balance bar plate, i.e. to vary the relative distance of the plate to the bottom plate. According to this patent, the plate remains horizontal, i.e. parallel to the general plane of the bottom plate. Thus the watchmaker who adjusts the balance shake has to act on the three regulating screws by repeatedly rotating them in succession until the plate reaches a height that defines a proper shake for the balance. This is a significant drawback for assembling the timepiece and adjusting the balance shake. Moreover, three regulating screws increase the cost of the timepiece and their arrangement at the periphery of the tightening screw requires relatively large dimensions for the base of the bar. This raises a problem as to the design of the timepiece movement and in particular as to the arrangement of the balance bar.
A timepiece sold by the Rolex company is also known that has a system for adjusting the balance shake. In this timepiece, the balance bar is of the double type, i.e. having two bases arranged at the two ends of the bar plate and allowing the balance bar to be rigidly secured on either side of the bearing arranged substantially at the centre of the plate. The two bases are respectively secured to the bottom plate by two tightening screws. Each of the two tightening screws is screwed inside a cylinder driven into the bottom plate. This cylinder has an interior threading for the tightening screw and an exterior threading for an adjusting nut. The two bases of the balance bar are held abutting against the two nuts by the two tightening screws. A friction spring formed by a resiliently deformable washer is provided underneath the nut so as to hold the latter in position when it is not being actuated by a watchmaker. The two tightening screws are respectively provided at the periphery of the two respective bases so as to allow the adjusting nuts, which have flutes on the external lateral surface, to be rotated in order to facilitate activation thereof using a suitable tool and thus adjusting of the balance shake.
The system for adjusting the shake of a balance described above has certain drawbacks. First of all, it is relatively complex and expensive. Indeed, this system comprises two cylindrical parts, with an inner threading and an outer threading, which have to be driven into the bottom plate. Moreover, the system comprises two fluted adjusting nuts. Then, in order to adjust the height of the bar plate with the balance in place, the tightening screws have to be provided on the outer edge of the two bases and a free space must be left on the periphery of the two tightening screws in order to allow access to the adjusting nuts which come out laterally underneath the bases. This regulating system is thus relatively complicated and limits the possibilities for arranging the balance bar in the timepiece movement.
It is an object of the present invention to propose a device for adjusting the shake of a rotating part in a timepiece, in particular a balance, which is relatively inexpensive and enables the shake of the rotating part to be efficiently adjusting, without increasing the size of the bar concerned or limiting the arrangement of its peripheral area.